Especially, read the passage from Honen Shonin in that post and the highlighted words because they guide you to other important articles. As I said there, if your body is ill, take whatever medicine available, lets say that you may use some breathing techniques or mental and physical relaxation exercises which do not contain any spiritual or religious elements, but in spiritual and religious matters, say the Nembutsu of faith exclusively.
Generaly speaking, various meditations imply various states of mind to be developed. If those states of mind to be cultivated make you depart from "clinging to Amida's sleeves" as Rennyo said, (from focusing your attention on Amida Buddha) then don't do it. If they contain some religious elements related with various divine figures or symbols outside of the Buddha Dharma, don't do it. If they imply relying on other Buddhas than Amida, don't do it, too. I am sure that Honen, Shinran and Rennyo knew about various practices for health in the Japanese Buddhism; they also knew about Yakushi Nyorai and the benefits of chanting religious formulas associated with Him, and they also became sick from time to time. However, they never quit the Nembutsu of faith, nor mixed it with those practices. They used medicine and took treatment prescribed by doctors, but never did anything religious or spirtual for healing. Of course, again, not all breathing techniques or relaxation methods contain religious or spiritual elements! So, I am not against such tehnicques, if they do not fall in the category explained above.
But zazen for example, no matter why you practice it, cannot trully accompany the Nembutsu of faith. I explained why in this article, We cannot mix Nembutsu with zazen and here, too: My answer to a comment comparing Zen with Jodo Shinshu
So, it depends on each person. Some people may claim that they only practice this or that meditation for health reason, when in fact, they are unconsciously bored with the Nembutsu. Not all those who try various meditations are really practicing them for health benefits only. I can tell you from my experience as a priest, that many people I met and who became interested in meditation, even just for relaxation, as they said, gradually departed and estranged themselves from the Nembutsu. Human mind is unpredictable and unstable, and it does not like to stay in a single place, especially if it is not well established in faith.
After all, every sincere follower should know where is the red line between relaxation and health, and spiritual/religious practice.
This is all. I have nothing more to say on this topic. Just look into your mind and decide for yourself what to do and be careful to be in accord with the Primal Vow. Nothing more is important than this. As Honen advised, do whatever does not hinder your from saying the Nembutsu. Abandon whatever hinders you in saying the Nembutsu.
Best wishes! Namo Amida Butsu
I'm actually a lousy meditator and I'm not even tempted by meditation. I never could do it... I tried and tried... I even went to live in a Zen temple in Japan for some time, and realized I would die if I have to sit for 10 hours zazen a day. So I abandoned that completely.
However hypothetically I was interested in the question... because really, if someone practices for neurological, health reasons, then at least theoretically, there shouldn't be anything wrong with it.
But I failed to think of the possibility that one might get tricked by one's unconscious mind into believing "it's just for health" when really it's something else. I haven't considered this option. Thank you for reminding me of that possibility.
After reading your reply, I would say it's best to stay away from all meditation that is rooted in religion, even if it was artificially secularized. For instance, yoga practice as it is done in the West was stripped from all religious symbols. Even though it was initially connected to the god Śiva. But anyway they chant "OM" even if they don't talk about the meaning. So the religious component is still there. It's best to stay away and leave it all to Amida.
Namo Amida Butsu